The use of magenta couplers comprising 1-phenyl-3-anilino-pyrazoto-5-one couplers containing phenylthio coupling-off groups at the 4-position are well known in the art. See for example U.S. Pat. No. 4,853,319 of Krishnamurthy et al. and other patents cited therein. While elements employing such couplers have provided certain advantages, there remain several shortcomings in photographic elements relying on these types of magenta couplers.
These shortcomings relate to the dye-forming efficiency of the coupler, the speed with which the dye is formed, the dye hue, and the undesirable occurrence of staining during processing.
The hue of the dye obtained upon completion of the coupling reaction is important because it affects the accuracy of color rendition and also impacts the printer's ability to produce an accurate print from the negative produced from the original exposure. The hue of the dye is a function of the compositional make-up of both the parent and the coupling-off group. Both the individual substituents and the combined effect of the different substituents selected can affect the hue. The parent substituents affect hue primarily through their affect on the chromophore of the dye while the coupling-off group substituents have a more indirect effect by influencing the local environment of the dye, particularly when the coupled-off group is not free to diffuse away from the dye and into the hydrophillic phase.
Additionally, staining or nonimagewise coloration of the element is to be avoided. One way that staining can occur is through the phenomenon called continued coupling. Certain couplers are more prone than others to react with oxidized developer that is carried over with the film into the bleach bath. These couplers will then undesirably form dye on a nonimagewise basis causing a magenta stain.
The speed and efficiency with which the dye is formed can present added problems. When a coupler undergoes coupling with a color developer to form a dye, the coupler goes through an intermediate stage wherein the oxidized developer and the coupling-off group are both annexed to the coupler parent. This intermediate is a leuco dye which is uncolored until the coupling reaction is complete. In the ideal photographic element, the intermediate stage is essentially instantaneous so that the process of dye formation is completed during development. The presence of the semi-stable leuco dye can effectively reduce dye density and adversely affect color rendition in the printing step. Moreover, the presence of the semi-stable leuco dye can lead to post processing density increases the extent of which cannot be predicted and this leads to the undesirable situation of having an image which changes with time. Thus, the formation of semi-stable leuco dyes needs to be avoided.
The dye forming efficiency of the coupler is affected by many factors such as the extent to which the parent portion of the coupler is ballasted so as to retain its proper position in the photographic element in order to optimize the image recorded. If the coupler parent is not sufficiently ballasted, it is free to wander both horizontally and vertically during processing thereby adversely affecting both sharpness and color rendition. Moreover, the coupler is susceptible to being washed out of the element entirely and thus contributing no dye density to the image. Therefore, this problem is to be avoided.
While various efforts have been made to provide improved couplers, none have succeeded in solving the foregoing problems.
U.S. Pat. No. 4,463,085 suggests a way to reduce the amount of unwanted staining that occurs during processing. Elements containing 1-phenyl-3-anilino-pyrazolo-5-one or 1-phenyl-3-acylamino-pyrazolo-5-one couplers containing phenylthio or other types of coupling-off groups at the 4-position are employed in combination with certain piperidine compounds in order to prevent such staining. The materials exemplified therein do not provide the desired properties such as diffusion resistance of both the parent and coupling-off group. Compound I-28 has the formula: ##STR2## This coupler contains a ballasted parent with a sulfonyl substituent but does not contain a carbonamido substituent in the coupling-off group in a position ortho to the sulfur on the phenyl ring. It does not provide the desired photographic properties in that the presence of the ortho alkoxy substituent on the coupling-off group causes the undesired formation of semi-stable leuco dye which leads to post processing density increases. Research Disclosure 16736, March 1978 discloses parent groups having a hexadecylsulfone in the 4-position of the anilino ring but does not disclose the combination with the coupling-off group of the invention nor the advantages to be obtained thereby.
U.S. Pat. No. 4,994,359 relates to pyrazolone couplers having improved color density and reduced dye staining. These benefits are said to be obtained through the inclusion of a dialkyl amine compound with a pyrazolone coupler having an arylthio coupling-off group which includes a carbonamido substituent in the position ortho to the sulfur. Examples of two of the couplers exemplified (M-4 and M-5) are as follows: ##STR3## These couplers contain sulfonamide and sulfamoyl substituents, respectively, on the parent anilino groups. For these couplers, the log P of the coupling-off group is inadequate to prevent the undesired wandering of the coupling-off group and corresponding silver development effects. Moreover, the sulfonamide substituent provides inferior properties with respect to hue when compared to the alkyl- or arylsulfonyl substituents of the present invention. U.S. Pat. No. 4,835,319 suggests a coupling-off group having the formula: ##STR4## however, it is not suggested to increase the log P and to then employ the coupling-off group with a sulfone containing anilino pyrazolone parent in order to solve the problems of the art.
It is therefore a problem to be solved to provide photographic elements containing a magenta coupler which do not present problems associated with photographic properties such as the dye-forming efficiency of the coupler (including silver development inhibition), the speed with which the dye is formed, the dye hue, and the undesirable occurrence of staining during processing.